(1) Field of the Invention
The present invention relates to a method for detecting a reference angular position of a rotary body such as the crankshaft of an internal combustion engine mounted on a motorcycle.
(2) Description of a Related Art
A system for detecting a reference angular position of a rotary body is shown in FIG. 1, which system has been disclosed in a Japanese Utility Model Application No. 62-32216 filed by the same applicant as the present application. As shown, two magnetic projections 2a and 2b are formed distantly from each other on the periphery of a rotary body 1 along the circumferential direction thereof. Two detectors 3a and 3b are formed in the vicinity of a locus of the two magnetic projections 2a and 2b. The detectors 3a and 3b respectively produce output signals having waveforms respectively shown in FIGS. 2A and 2B. The two output signals are supplied through diodes 4a through 4f and inverters 6a and 6b to AND gates 5a, 5b and 5c which respectively produce reference angular pulses P.sub.1, P.sub.2 and P.sub.3 having waveforms respectively shown in FIGS. 2C through 2E.
However, it has been revealed that the output signals Paa and Pbb of the detectors 3a and 3b do not necessarily appear at the same time but appear with a certain time difference even at a timing when the reference angular pulse P.sub.2 appears, as seen from FIGS. 3A and 3B. This is because some manufacturing errors inevitably exist in the arrangement including the magnetic projections 2a and 2b and the detectors 3a and 3b. Because of the time difference between the pulses Paa and Pbb, there appear the pulses P.sub.1 and P.sub.3 from the AND gates 5a and 5c before and after the pulse P.sub.2. These pulses P.sub.1 and P.sub.3 cause erroneous detection of a reference angular position in the later stage such as an ignition timing controller (not shown).
It has further been revealed that erroneous detection of the reference angular position will take place due to a reverse rotation of the rotary body in case the rotary body is the crankshaft of the motorcycle.